1. Field of the Invention
The present invention relates to the use of agents in the treatment of machines for the manufacture of pulp, paper, and cardboard to clean these units of adherent impurities of natural resins and/or synthetic polymers and to prevent soiling of these units by such impurities.
2. Description of the Background
In the production of pulp and paper suitable measures are required to prevent agglomeration and deposition of resin portions of wood, adhesive portions from waste paper, and plastics portions in the recycling of latex-coated waste paper, in order to avoid disturbances in production and impairment of the pulp or paper quality.
According to EP 517 360 A1 inhibiting mixtures of surfactants and solvents, preferably fatty alkanolamides, ethoxylated compounds, aliphatic hydrocarbons, and orange-terpenes, are added to the pulp suspension in an amount of 1-200 ppm. However, the agents such used are insufficiently effective; for this reason the manufacturing process must frequently be interrupted to clean machine parts, in particular the wire and press section; according to EP 178 340 B1 only limonene is used as solvent.
According to EP 235 01 5 A1 and EP 599 440 A1 resin sedimentations may be prevented by cationic polymers based on epichlorohydrin and amines, or by simultaneously using nonionic surfactants.
U.S. Pat. No. 4,190,491 and U.S. Pat. No. 3,582,461 describe copolymers and dicyandiamide-formaldehyde condensates whose effectiveness is also based on the interaction with anionic resin components in the pulp suspension. The ionogenic components are neutralized and dispersed, or already existing deposits are redispersed, without restricting the activity of cationic retention agents, as in the case of anionic dispersion agents.
However, the applicability of dispersing agents in closed-circuit water cycles is limited since the dispersed resin portions are not completely bound to the anionic pulp fibers and then discharged, therefore they remain in the industrial process water to an increasing extent.
Because deposits of tacky materials cannot sufficiently be prevented from depositing in papermaking machines, it is proposed in EP 359 590 B1 to lay on the device surfaces an aqueous solution of cationic polymers together with a water-soluble, nonionic or cationic surfactant.
A similar application with selective treatment of wires and felts in papermaking machines is carried out according to the "Daraspray-conception" which is described by T. Hattich, T. Hassler, and G. Corbel in "Wochenblatt fur Papierfabrikation" 122, 1994, pages 644-648.
The disadvantages of this method are characterized by the fact that the forming coating layer depends on the equilibrium concentrations of the water-soluble components in the system, and that the brown-colored, elastic structure of the protective film becomes hard and brittle in case of insufficient moisture. Another disadvantage results from the very specific dosage of several components which is sometimes necessary to form the coating.
Furthermore, EP 550 230 A1 proposes to clean the felts of the press section by using fatty acid imidazolines; and according to EP 647 737 A1 these compounds are used together with ethoxylated nonylphenols and special sulfonates to prevent depositions of polyamidoamine-epichlorohydrin resins in felts. EP 0 648 820 A2 describes compositions which are used to remove toners from paper surfaces, adhesive residues from plastics, to peel plastics coatings, and to cleanse metal surfaces from cutting oil residues or color pencil marks, as well as to remove PVC-portions secured by means of adhesives. In this connection, concentrated oil-in-water emulsions having a nonaqueous phase portion of 8-90%-wt. are used that comprise various kinds of organic compounds, such as dicarboxylic acid diester, and which are used under partial application of ultrasound and further aids (unwoven fabric strips) in the temperature range of 5.degree.-70.degree. C., i.e. partially under additional heating of the cleaner, during the cleaning operation. The emulsions additionally comprise solvents, such as isopropanol, toluene, benzyl alcohol, methyl ethyl ketone, N-methyl-pyrrolidone, di- and triethylene glycol dimethyl ether, and 3-methyl-3-methoxy butanol, which limit the application of these emulsions in closed systems for reasons of occupational safety and health hazard.
However, particularly in papermaking using waste paper, the inhibitory action of these known agents is insufficient, since tacky components of the recycling raw material, in particular at temperatures above 50.degree. C., are still deposited as finely dispersed system in the pulp suspension, first in dissolved state and then in the form of agglomerates (stickies) on the surface of the machines, in particular wires, felts, cylinders, and guide rolls. This affects the paper quality by formation of stains and holes; the production process is disturbed by breaking of the pulp or paper webs; and there are disturbances in the drainage of the pulp suspension, in sheet formation due to decreased water permeability and water absorption of the wires or felts, as well as in drying due to reduced heat transfer.
Since the described auxiliary agents are insufficiently effective, it is still necessary at present to clean the stopped or slowed-down pulp and paper machines with chemicals which are sprayed, for instance, and rinsed off with water together with the dirt particles after a certain period. Moreover, it is known to clean wires in continuous, separate wire-cleaning plants wherein cleaning is not always satisfactory, too. Other methods avoid these disadvantages by using wire materials specially coated with Teflon or other plastic materials; however, these are mechanically vulnerable and costly.
Moreover, the use of specific oil-in-water emulsions as microbicide substitute in papermaking is known from DE 43 40 665 A1.
Accordingly there was the object to eliminate the disadvantages described in detail above, and in particular to find agents for this purpose which, when used in the manufacture of pulp, paper, and cardboard using waste paper to treat pulp, paper and cardboard-making machines, are suitable to clean the machinery from adherent agglomerates of synthetic polymers and natural resins and/or to prevent adherence of these substances on surfaces of the machines.